Rational : For its benefits, physical activity should be encouraged in individuals living with type 1 diabetes (T1D) but is limited by the fear of hypoglycemia. People treated with continuous subcutaneuous insulin infusion (insulin pump) have the option to temporarily reduce basal insulin infusion rate. For an exercise practiced in the late post-prandial phase, this is the preferred method for preventing exercise-induced hypoglycemia, but no study has validated the optimal timing to reduce basal insulin infusion. Objective: To compare the efficacy of three timings to decrease basal insulin infusion rate by 80%, either at the start (T0), 20 minutes (T-20), or 40 minutes (T-40) before a 45-min exercise on a stationary bicycle at moderate intensity (60% VO2peak) performed 3 hours after a standardized meal. Results: No significant difference between the three strategies in terms of percentage of time spent under 4.0 mmol/L and time spent between 4.0 and 10.0 mmol/L was observed. With a reduction at T-40, although not significant, the glucose level at exercise onset was higher, fewer participants needed additional carbohydrates before and during exercise, and the time to first hypoglycemia was longer in comparison with T0 and T-20. Conclusion: In people living with T1D and treated with an insulin pump, an 80% reduction in basal insulin infusion 40 minutes before a 45-min moderate intensity exercise practiced in a late post-prandial state is not enough to reduce hypoglycemia. Further studies are needed to determine whether this reduction should be greater, earlier and/or combined with carbohydrates.